1. Field of the Invention
This invention relates generally to heterocyclic polymers. In particular it relates to polybenzimidazoles where chain extension occurs through an arylene substituent on the substituted nitrogen of the benzimidazole ring.
2. Description of the Related Art
Polybenzimidazoles (PBI) are heterocyclic polymers commonly prepared by the condensation reaction of an aromatic bis(o-diamine) with an aromatic diacid or derivative thereof and having a repeat unit of the general structure ##STR1## where Ar is a tetravalent aromatic radical such as 1,2,4,5-tetrasubstituted benzene. Ar may also be a bis(o-diphenylene) having the general structure ##STR2## where Z.dbd.nil, O, S, SO.sub.2, C.dbd.O, CH.sub.2, or any other appropriate divalent radical. Ar' is a divalent aromatic radical which may be 1,3-phenylene, 1,4-phenylene, 4,4'-biphenylene, 4,4'-oxydiphenylene, 4,4'-sulfonyldiphenylene, or any other appropriate divalent radical.
The synthesis and characterization of PBI has been extensively studied and documented. Reviews on PBI are available. (A. Buckley, D. E. Stuez, and G. A. Serad, Encyl. Poly. Sci. Tech.,Vol. 11, 2nd ed., 1988, p. 572; P. E. Cassidy, "Thermally Stable Polymers", Marcel Dekker, Inc., New York, 1980, p. 163.) The first reported synthesis of PBI involved the reaction of aliphatic dicarboxylic acids with aromatic bis(o-diamine)s [K. C. Brinker and I. M. Robinson, U.S. Pat. No. 2,895,948 (Jul. 21, 1959)]. Since then several methods have been utilized in their preparation. Each method will be briefly mentioned with an accompanying reference. The most common synthetic method of PBI involves the melt condensation of aromatic bis(o-diamine(s)) with aromatic diacids or derivatives thereof [H. Vogel and C. S. Marvel, J. Polym. Sci., 50, 511 (1961 )]. PBI has also been prepared in polyphosphoric acid [Y. Iwakura, K. Uno, and Y. Imai, J. Polym. Sci., Part A, 2, 2605 (1964)] and in sulfolane or diphenylsulfone [F. L. Hedberg and C. S. Marvel, J. Polym. Sci., Poly. Chem., 12, 1823 (1974)] from aromatic bis(o-diamine)s and aromatic diacids or derivatives thereof.
Another preparative route involves the reaction of aromatic bis(o-diamine)s with the bis(bisulfite adduct)s of dihaldehydes [J. Higgins and C. S. Marvel, J. Polym. Sci., Part A-1, 8, 171 (1970)]. The alkoxide catalyzed reaction of aromatic bis(o-diamine)s with dinitriles is another synthetic route [D. I. Packham, J. D. Davies, and H. M. Paisley, "Polymer, 10, (12), 923 (1969)].
PBIs where the hydrogen atom on the nitrogen atoms of the benzimidazole ring are replaced by phenyl groups have been prepared from the reaction of bis(o-anilinoamino) arylenes with aromatic dicarboxylic acids or derivatives thereof. [H. Vogel and C. S. Marvel, J. Polym. Sci., A 1, 1531 (1963)]. The resultant polymers exhibited slightly better thermal oxidative stability than unsubstituted PBIs; however, they were too thermoplastic to be useful.
PBIs where chain extension occurs through the arylene substituent on the substituted nitrogen of the benzimidazole ring are a variation of the phenyl substituted PBIs called poly(N-arylenebenzimidazole)s (PNABIs). They were prepared in high molecular weight from the melt reaction of the diphenyl esters of aromatic dicarboxylic acids with bis(o-aminoanilino) arylenes. [A. A. R. Sayigh, B. W. Tucker, and H. Ulrich (Upjohn Co.), U.S. Pat. No. 3,708,439, Jan. 2, 1973)].